Coating agent for corrosion-resistant coatings

Abstract

The invention relates to a multicoat paint system comprising, lying above one another in this order,(1) at least one first basecoat comprising basecoat material (A),(2) preferably a second, color and / or effect basecoat comprising basecoat material (B), and(3) at least one transparent coating comprising clearcoat material (C),wherein the basecoat material (A) which forms the first basecoat comprises at least one binder (a.1), at least one color and / or effect pigment (a.2), and a corrosion-inhibiting component (a.3) with a parent structure (GK1), selected from the group of low molecular mass alkyl, aryl, aralkyl, and cycloalkyl radicals and / or heterocyclic radicals, which carries at least one phosphoric acid group as ligand (L1), and / or at least one corrosion-inhibiting component with a parent structure (GK2), selected from the group of alkyl, aryl, aralkyl, and cycloalkyl radicals, heterocyclic radicals and / or polymers, which carries at least one phosphonic acid group as ligand (L2).

Description

FIELD OF THE INVENTION [0001]The present invention relates to coating compositions for corrosion-stable finishes, more particularly for multicoat color and / or effect paint systems.PRIOR ART [0002]Modern motor vehicles commonly sport multicoat color and / or effect paint systems. Generally speaking, these multicoat paint systems comprise an electrocoat, a surfacer coat, anti-stonechip primer or functional coat, a color and / or effect basecoat, and a clearcoat. The multicoat paint systems are produced preferably by means of what are called wet-on-wet processes, in which a clearcoat film is applied to a dried, uncured basecoat film, and then at least basecoat film and clearcoat film are jointly cured thermally. This process may also be extended to include the production of the electrocoat and the surfacer coat, anti-stonechip primer or functional coat.[0003]In these systems, the surfacer coats, anti-stonechip primers or functional coats are critical for such essential technological proper...

AI Technical Summary

Benefits of technology

[0027]In light of the prior art it was unforeseeable for the skilled worker that the problems addressed by the present invention, of reducing the blister corrosion in combination at the same time with improved adhesion between basecoat comprising basecoat material (A) and primer (G) respectively to the free metallic substrate, could be achieved by means of the multicoat paint system of the invention. The thermally curable aqueous basecoat material (A) used in accordance with the invention could be prepared in a simple manner based on conventional commercial aqueous basecoat materials and produced first color and / or effect basecoats (A) which, even at a film thickness <15 μm, were able fully to replace conventional surfacer coats, anti-stonechip primers or functional coats, without adversely affecting the performance properties of the multicoat paint systems, more particularly, the stonechip protection and UV stability even after long-term exposure. At the same time it was possible to implement the aqueous basecoat material (A) on existing lines for the application of basecoat materials by electrostatic spray application and pneumatic spray application, without necessitating conversions.

[0072]The corrosion-inhibiting component (a.3) comprises at least one phosphoric acid group as ligand (L1), attached to a parent structure (GK1), and / or at least one phosphonic acid group as ligand (L2), attached to a parent structure (GK2), which allows effective adhesion to the metallic substrate, and is able, with the metal ions that are released in the corrosion of the substrate, to form chelates (regarding “chelates”, compare Römpp Online, Georg Thieme Verlag, Stuttgart, New York, 2005, entry “Chelates”). When the multicoat paint system is thermally cured, the ligand (L) does not lose its capacity as a chelating agent.

[0073]Through complexation and / or occupation of the metal surface, the ligand (L) inhibits the corrosion, by reducing the proportion of the metal surface that is freely accessible for the corrosion, and / or bring about a shift in the electrochemical potential of the half-cell formed at the metal surface. Furthermore, component (a.3) is additionally able, through a buffer effect, to suppress the shift in pH of the aqueous medium, at the interface with the metal, that is necessary for corrosion.

[0106]The resulting coating systems are of outstanding automobile quality. In addition to an outstanding stonechip resistance, they exhibit excellent adhesion to the primer (G) and to the subsequent coating films, and also, in particular, outstanding resistance to corrosive undermining and resultant blister corrosion of the multicoat systems in the vicinity of bare areas such as those produced, in particular, by stone chipping.EXAMPLES

Problems solved by technology

Where the above-described multicoat paint systems are exposed to stone chipping, there are instances, in spite of their high stonechip resistance, of flaking of the overall coating system, and in such cases the bare metallic substrate is exposed and is subjected to attack by corrosion.

This corrosion is manifested in the formation of blisters, which are bubblelike eruptions in the multicoat paint system, accompanied by progressive enlargement of the area exposed by the stone chipping, as a result of the corrosive undermining of the multicoat paint system starting from the corrosion on the bare metallic substrate.

Low molecular mass corrosion inhibitors can only reach the interface between substrate and paint, and hence be deposited, in the deposition process when they carry a positive charge; corrosion inhibitors of this kind usually have an adverse effect on the properties of the overall paint tank and hence of the finish.

In general, the particle size of pigmentlike corrosion inhibitors means that they have very little mobility or none at all.

Moreover, the application properties of the coating compositions described in DE 103 00 751 A1 can be adapted only with high cost and complexity to the application conditions, particularly with regard to the rheology, of the kind that are necessary for the above-described multicoat paint systems in automotive OEM finishing.